1. Field of the Invention
The present invention relates to an improvement of a paper resupplying device installed in an image forming apparatus capable of superposing copy images on one side of a paper and forming an image on both sides of the paper, that is forming a so-called composite image.
2. Description of the Prior Art
In order to form a so-called composite image on one side or both sides of a paper, a paper resupplying device in an image forming apparatus has been provided with an intermediate tray for stacking papers after forming one image thereon and a paper discharging device for discharging the papers onto the intermediate tray after the one image is formed thereon, such that the papers descend forwardly during such discharge.
In such paper resupplying device, if the distance between a paper discharging position from the paper discharging device and the intermediate tray is increased, the quantity of papers stacked in the intermediate tray can be increased, and thus jamming easily can be corrected.
However, when the papers discharged from the paper discharging position descend forwardly, due to a thermal effect in a preceding fixing operation or treatment, the possibility exists that simultaneously both corner portions of the leading end of each paper are bent downwardly toward the lower surface thereof. Thus, opposite corner portions (c) of the leading end (d) of the paper (a) curl downwardly causing leading end (d) of the paper to curl under rearwardly. Thus, the paper takes the shape of turned-over letter "C" as seen from the leading end of the paper and the paper is discharged under the condition that it descends forwardly an curls under rearward, as shown in FIG. 8.
If the distance from the paper discharging position to the intermediate tray 21 is increased to increase the quantity of papers (a) stacked and to take correction of jamming into consideration, there occurs the further possibility that the flat leading end (d) will engage with the intermediate tray 21 at a right angle with a surface of the tray or will be rolled rearwardly at corner portions (c). As a result, not only does the leading edge of the flat end (d) and both corner portions (c) of the paper cause increased conveying resistance, but also the papers (a) are discharged successively under a condition such that they tend to fall forwardly and roll under rearwardly, such that jamming occurs.
In case particularly of small size papers, a curled portion is larger proportionally than a non-curled portion, in the width-wise direction, compared with large size papers. Thus, the above described turned-over letter "C" condition can approach a "O" letter condition. That is, the condition of falling forward and curling under becomes even more notable.
Also, there has been proposed a paper discharging device including a plurality of paper discharging portions for discharging papers to the intermediate tray, with the respective paper discharging portions other than that on the downstream end in the paper discharging direction being provided with a paper discharging guide movable to a posture allowing papers to pass in the downstream direction.
The paper discharging portions in this type of paper discharging device generally are provided at three places, for example an upstream end, a downstream end and a midway position in the paper discharging direction. Large size papers are passed to the intermediate tray by moving the upstream end to said paper discharging guide to the paper discharging posture thereof. Middle size papers are passed to the intermediate tray by moving the middle paper discharging guide to the paper discharging posture thereof. Small size papers are passed to the intermediate tray from the downstream paper discharging portion by moving both of the paper discharging guides to postures thereof allowing the papers to pass.
In a paper resupplying device provided with paper discharging device having such construction, a reduced distance between the paper discharging device and the intermediate tray has been employed to avoid curling downwardly of small size papers which are discharged to the intermediate tray under the worst conditions, as a standard.
However, if such distance is reduced in such manner, a disadvantage occurs in that it is difficult to correct jamming occurring between the paper discharging device and the intermediate tray.
Also, there has been proposed a device provided with distance changing means to widen such distance as needed. However, problems result in that not only is the device of a large size and manufacturing costs are increased, but also jamming occurs if an operator forgets to return the distance changing means to the original distance.